As tensions between Russia and Ukraine increase, the Russians are moving state-of-the-art S-400 Triumph air-defense missiles into Crimea, which the Russians annexed in 2014. Russia claims the Ukrainians are planning to retake the peninsula by force.

The BBC relates statements in Russian media that the Triumph system was earmarked for delivery to Crimea last month and would be used in forthcoming “exercises.” A similar system was deployed to protect Russian assets in Syria after Turkey shot down a Russian warplane in November.

According to Russian news agencies, the missiles were tested at the Kapustin Yar test range in southern Russia before delivery to the air defense regiment in Crimea. They are “designed to hit airborne targets at a range of up to 400km (249 miles) and ballistic missiles at a range of up to 60km, flying at speeds of up to 4.8km per second.”

Ukraine claims there are now 40,000 Russian troops massed along the Crimean border, prompting Ukraine to call its own forces to the highest state of alert.

Bloomberg News reports world powers are urging Russia and Ukraine to “refrain from ratcheting up a confrontation over Crimea.” The Europeans are notably skeptical of Russia’s claims that Ukraine tried to slip saboteurs into Crimea for terrorist attacks.

“We reiterate our condemnation and non-recognition of the illegal annexation of Crimea. There has been neither concrete evidence provided by Russia sustaining its claim nor any independent confirmation of the claims made by Russian authorities,” said European Commission spokesman Alexandre Polack on Friday.

The U.S. State Department acknowledged “this is a very tense time” and called on both sides to “take a step back” and reduce tensions.

However, Russian Prime Minister Dmitry Medvedev said Russia was considering the termination of diplomatic ties with Ukraine and insisted the alleged Ukraine incursion into Crimea was “a crime that needs to be investigated.”

Bloomberg also notes that Russian President Vladimir Putin surprisingly “dismissed his long-time ally and chief of staff, Sergei Ivanov, on Friday,” replacing him with the much younger Anton Vaino, part of a new corps of young officers who have grown up knowing nothing but Putin’s rule.

Ivanov was “one of the handful of officials who worked on operations in Crimea, eastern Ukraine and Syria.” His dismissal could signal a change in Russian posture regarding Crimea and Ukraine.

The Economistjoins Bloomberg News in noting that August is historically the month when Russia prefers to commit acts of aggression, while Western leaders are largely on vacation, and the U.S. is bearing down on a presidential election. Russia has parliamentary elections coming in September, and the Kremlin is nervous about public discontent with a protracted economic crisis. A war against “terrorists” and “fascists” in Ukraine might be just the thing to take Russian voters’ minds off that gloomy economy.